     [t1,x]=ode45('shier1',[0 15],[25 2]);         
     [t2,y]=ode45('shier2',[0 15],[25 2]);   
     x1=x(:,1);x2=x(:,2);
     x3=x2./(x1+x2);
     y1=y(:,1);y2=y(:,2);
     y3=y2./(y1+y2);
     plot(t1,x3,'-',t2,y3,'*')
